This invention relates to the field of ionizers and specifically to an improved in-line gas ionizer. The in-line gas ionizer maintains an inherently balanced and contamination-free atmosphere, and thus suppresses electrostatic charge buildup within a target area or clean environment.
Electrically insulated objects and ungrounded metal objects may acquire built up electrostatic charge over time, which can range up to several thousand volts. Differences in local surface charge may also develop on insulated materials. The accumulation of electrostatic charge occurs for many reasons, including movement of objects and the accompanying friction, induction or receipt of charge from other objects, and contact with electrostatically-charged surfaces.
The accumulation of electrostatic charge can have undesirable effects in some instances. For example, the manufacture of electrical components such as integrated circuits can be adversely affected by electrostatic charge. Static charge can destroy the minute conductive paths in integrated circuits and can cause dust particles and other contaminants to accumulate on the circuits.
Integrated circuits are typically manufactured through a controlled process in a clean environment, wherein equal amounts of positive and negative ions are generated in order to reduce electrostatic charge and minimize airborne contaminants. Maintaining a high level of positive and negative ions in the air which surrounds electrical components in a manufacturing environment is one of the more effective techniques for suppressing electrostatic charge. A conventional air ionizer for generating positive and negative ions typically includes two or more high voltage electrodes which are situated a certain distance away from the objects which are to be electrostatically protected. The intense electrical field generated by an electrode causes a corona discharge, which acts to disassociate air molecules into positive and negatively charged ions. Ions with the same polarity as the charged electrode are repelled and disbursed outward, producing an available ion charge current. Electrodes of both polarities are provided in order to generate equal amounts of positive and negative ions. The electrodes are typically positioned close enough to the electrical components so that the ions will be attracted to the surface charges or come in direct contact with the components. A fan is often introduced into the system in order to generate airflow across the electrodes and further disburse the ions in a stream of air toward the electrical components that are to be electrostatically protected. These ions neutralize undesirable electrostatic charge.
The conventional fan-assisted, corona type air ionizer is not always appropriate in some modern clean room applications for several reasons. Integrated circuits are manufactured in an isolated mini-environment which can be limited in space, this makes the use of a fan for ion dispersion very difficult. Furthermore, the use of a fan for ion dispersion can also cause contamination problems such as emitter point erosion and the introduction of dirty particles from the fans.
Additionally, this type of fan-assisted, high voltage electrode air ionizer generates a significant electromagnetic field. This electromagnetic field can damage the integrated circuits if the fan-assisted, high voltage electrode air ionizer is positioned too close to the target integrated circuits. Finally, when using a conventional fan-assisted, high voltage electrode air ionizer, the high voltage electrodes must be positioned equidistant from the target integrated circuits in order to provide highly concentrated, equal amounts of positive and negative ions which are able to reach the target integrated circuits. If the electrodes are not equidistant from the target integrated circuits than more ions of one polarity may reach the circuits than ions of the opposite polarityxe2x80x94ex. if the positive electrode is closer to the target integrated circuits then the negative electrode than more positive ions may reach the target integrated circuits than negative ions. If this occurs, this may impart a charge to the circuits, thereby damaging them. In many environments it is very difficult, if not impossible, to achieve a perfect equidistant arrangement due to obstructions or size restrictions.
U.S. Pat. No. 4,827,371 granted to Yost discloses an alternative X-ray technique for providing both positive and negative ions toward a target area in order to reduce electrostatic charge and eliminate particulates in a clean air environment. The technique disclosed in Yost ionizes pressurized gas and delivers the ionizedgas to a target area where the charge and air contaminants are to be eliminated. However, the device disclosed in the Yost patent requires the continuous use of large volumes of pressurized gas in order to operate effectively. In addition to being costly, the large volume of ionized gas in Yost""s method is not efficiently managed in order to avoid recombination of the ions before the ionized gas reaches the target area. In Yost, the ionized gas is produced in high concentration in a relatively stagnant air chamber. The ions are not harvested or directed toward the target area quickly enough, resulting in ion recombination before the target area is reached. In addition, the device is cumbersome to implement and may be impractical for some applications. The present invention, as discussed below, overcomes the inherent limitations of Yost""s ionizing technique.
The method and apparatus of the present invention provide a continuous flow of clean, balanced, ionized gas into a target area in order to reduce electrostatic charge build up and protect electrical components in a clean environment. The unique design of this invention allows more efficient production and delivery of ionized gas toward a target area using a relatively or particularly small device. The ionized gas is directed at a sufficiently high velocity toward the target area, thereby eliminating electrostatic charges within the area and reducing ion recombination effects found in the prior art.
In one aspect of the present invention, a stream of pressurized gas is directed through an inlet channel into an ionization chamber, where the gas is ionized. The ionized gas is further directed out of the chamber, through an outlet port, and toward a target area at a high velocity. Within the inlet channel is a removable flow-regulating device which has a central restriction or orifice through which the pressurized gas is directed. The size of the central restriction or orifice controls the speed at which the pressurized gas is directed toward the ionization chamber. Moreover, the size of the oriface also affects dispersion of the gas within the ionization chamber as it enters the chamber. Since the flow regulating device is removeable, different flow regulating devices (each having a different size central restriction or orifice) can be used to regulate and vary the speed at which gas is directed into the chamber and achieve increased dispersion of the gas as it enters the chamber. Accordingly, flow speeds of gas through the ionization chamber can be achieved which are much greater than that attributable to using pressurization alone. Further, the gas can be dispersed more broadly as it passes through the oriface of the flow-regulating device and enters the ionization chamber. These features produce higher ionization yields and reduce ion recombination.
Another aspect of the invention allows previously ionized gas to be recirculated through the ionization chamber in order to supplement the pressurized gas which is directed into the ionization chamber through the inlet channel. Recirculation of previously ionized gas through the ionization chamber increase the total volume of ionized gas produced without requiring the exclusive use of expensive pressurized gas. As the pressurized gas is forced at a high velocity through the flow-regulating device and into the ionization chamber, a low-pressure area is created within the chamber. The size of the central restriction or orifice in the flow-regulating device controls the intensity of this low-pressure area. The low-pressure area is used to draw previously ionized gas from the target area through a return line, and back into the ionization chamber through a second inlet port, where it is once again ionized and mixes with the pressurized gas. An in-line filter may be used at the second inlet port to filter out any airborne contaminants, which may have been introduced into the recirculated gas drawn from the target area. The use of re-circulated gas increases the ionization effect of the in-line gas ionizer while reducing the volume of expensive pressurized gas that must be used.
In a further aspect, the present invention includes a miniaturized low level radiation source, such as a soft X-ray source, which ionizes the combined pressurized and recirculated gases as they flow through the ionization chamber. The miniaturized low level radiation source is compact and preferably as small as 1.5xe2x80x3xc3x973xe2x80x3xc3x974xe2x80x3 in size. The low-level radiation source emits soft X-rays into the ionization chamber through a transparent window. The transparent window is comprised of a thin polymer film. Use of a low level radiation source, such as a soft X-ray source, is less expensive and easier to shield. Moreover, soft X-rays will not penetrate the human skin or cause any health risks. An integral transparent window and seal arrangement allows the soft x-rays to pass into the ionization chamber while the device and outside air are isolated from the clean gas flow path. A leakproof seal is preferably used to secure the transparent window for optimum contamination control.